Sensors may be placed underground to detect a variety of conditions, for example, detecting and recording seismic signals, temperature, radiation levels, or the presence or absence of chemicals or gasses. The present inventors are aware that sensors have been placed into the ground using one of two methods. The first method is to dig a shallow hole, place a sensor in the hole and cover the sensor with earth so the sensor lies just beneath the surface. The second method is to place a sensor at the bottom of a well which has been cased.
The inventors have recognized that, in both conventional methods, sensors are subjected to unwanted conditions from the surface. In the first case, shallowly buried sensors are close to the earth's surface and therefore may be subject to detecting vibrational signals generated on the earth's surface, atmospheric temperature fluctuations and other surface conditions. In the second case, sensors at the bottom of a cased well may be mechanically linked to the earth's surface, and vibrations generated at the earth's surface may be transmitted to the sensors by the well's casing, or the casing may prevent detection of certain conditions such as the presence or absence of gasses.
The inventors have also recognized that tools used to drive items underground, for example, vibrational pile drivers or impact pile drivers, may damage sensors if used to directly place sensors underground.
Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings.